The present invention relates to the production of hydrocarbon mixtures of low sulfur content. More particularly, it relates to deep hydrodesulfurization of vacuum gas oils obtained from reduced-crude fractions of sulfur-containing crude oils and the production of hydrocarbon mixtures such as fuel oil, fuel oil blending stock, kerosene, diesel and fluid catalytic cracker feeds having low sulfur contents. In an especial aspect of the invention, fuel oil blends having a low sulfur content are produced in an integrated hydrodesulfurization process from vacuum gas oil (VGO) and vacuum residuum (VR) fractions of sulfur-containing reduced-crude oils. Other advantages obtained from the use of the present unique hydrodesulfurization process will be evident from the descriptions and examples herein.
Petroleum hydrocarbons are being used up at an everincreasing rate. New crude discoveries have not been sufficient to maintain the unproduced reserve. As a result, crude oils heretofore avoided where possible because of undesirable properties, especially those with high sulfur contents and those also containing heavy metal contaminants, must now be used as feeds for petroleum refineries. Asphaltenes frequently are found in combination with the metal contaminants and these together with sulfur and the metals are a source of serious processing and cost problems in the refining of such crude oils.
The dwindling world supply of crude oil makes it imperative that the refiners secure every last drop of useful hydrocarbon from a crude; and the need to do better in protecting the environment, for example by removing sulfur from combustion fuels, has made it evident that new and better processing methods and more select catalysts are needed. Better yields and reduced sulfur contents must be achieved. In particular, improvements in the processing of a vacuum gas oil from a reduced-crude feedstock are needed which in concert achieve:
1. a deeper desulfurization of vacuum gas oils, especially for the 350.degree. F. and higher boiling point hydrocarbon mixtures (atmospheric pressure) to at least to a sulfur content (weight percent) below about 0.2, preferably below 0.1, and most preferably below about 0.05; PA1 2. the use of hydrodesulfurization process temperature which is less than 850.degree. F.; PA1 3. a longer operating cycle for the catalyst in the hydrodesulfurization of a vacuum gas oil, e.g., a cycle of at least thirty months. PA1 4. a select high-activity vacuum gas oil hydrodesulfurization catalyst capable of deeper [item (1) above] sulfur removal and suitable for use with a combined feedstock, i.e., a mixture of vacuum gas oil and of vacuum-residuum gas oil, and the like; PA1 5. a vacuum gas oil hydrodesulfurization process performance permitting integration thereof with concurrent vacuum residuum hydrodesulfurization means for the substantial reduction of fuel oil pool sulfur content levels to new low levels, for example below 1 weight percent, and even to below 0.3 weight percent; PA1 6. a lower hydrogen gas consumption per unit of processed reduced-crude oil; and PA1 7. fuel oil products having acceptable stabilities. PA1 1. a hydrogen partial pressure in the range 300 to 800, preferably 350-650 psig; and PA1 2. a temperature in the range 550 to 850.degree. F. PA1 1. The use of the 350.degree. F.+ boiling fraction of the sulfur-reduced vacuum gas oil produced as described above as a blend stock for upgrading a sulfur-reduced vacuum residuum fuel oil; PA1 2. The use of all or a portion of a sulfur-reduced vacuum gas oil produced as described above as a feed for a fluid catalytic cracker (FCC) unit, particularly the 650.degree. F.+ boiling fraction; PA1 3. The production of a C.sub.4 + boiling range sulfur-reduced vacuum gas oil produced as described above, separating the resulting sulfur-reduced vacuum gas oil by fractional distillation into: PA1 4. Still further embodiments of the present invention will be evident from the Figures below and the description. PA1 1. a hydrocarbon product mixture having a sulfur content in the range, broadly, of 0.005 to 0.2 weight percent, particularly 0.1 to 0.005, and most particularly 0.1 to 0.05; PA1 2. a run cycle, hrs., in the range 8,000 to 30,000, usually greater than 24,000; and PA1 3. a hydrogen consumption which is in general less than required in a conventional process. PA1 1. comprise cobalt, molybdenum, and alumina; PA1 2. have an average pore diameter in the range 80-120 Angstroms (see U.S. Pat. No. 3,684,688 for background details with respect to average pore diameter determinations and other references); PA1 3. have an atomic ratio of cobalt to molybdenum in the range 0.3 to 0.6, preferably about 0.4; PA1 4. have a pore volume at least 0.5 cc per gram; and PA1 5. are sulfided, either prior to use or during process operation. PA1 1. calcining an alumina (no previous calcination experience above about 1700.degree. F.) support at a temperature in the range 1400.degree. to 1700.degree. F.; PA1 2. impregnating the calcined alumina with an aqueous solution of a cobalt salt and a heteropolyphosphomolybdic acid; and PA1 3. sulfiding the composite prior to use by ordinary means or in situ in use by contacting of a sulfur-containing feed, as herein, with the composite under hydrodesulfurizing conditions.